In the electronics industry, a continuing goal has been to reduce the size of electronic devices, such as camcorders and portable telephones, while increasing performance and speed. Integrated circuit packages for complex electronic systems typically have a large number of interconnected integrated circuit chips. The integrated circuit chips are usually made from a semiconductor material such as silicon or gallium arsenide. The various semiconductor devices on the integrated circuit chips are formed in various layers on the chips using photolithographic techniques. After manufacture, the chips are typically incorporated into packages that are then mounted on printed circuit wiring boards.
Integrated circuit chip packages typically have numerous external pins that are mechanically attached by solder or a variety of other known techniques to conductor patterns on the printed circuit wiring boards.
Typically, the packages in which these integrated circuit semiconductor chips are mounted include a substrate or other chip mounting device. One example of such a substrate is a leadframe. High performance leadframes typically are multi-layer structures including power, ground, and signal layers that may be on separate planes.
More particularly, a leadframe is a metal frame that includes a centrally located die paddle or die pad and a plurality of peripherally-located leads that surround the die pad. The die pad mounts the semiconductor chip (or “die”). Power, ground, and/or signal leads of the leadframe are connected electrically by wire bonds to power, ground, and/or signal sites on the chip and serve as external connecting means for the chip.
After the chip is wire-bonded to the leads, the chip, the die pad, and portions of the leads are encapsulated in a plastic, an epoxy-molded compound, or a multi-part housing made of plastic, ceramic, or metal, to form the semiconductor package. The package protects the leadframe and the chip from physical, electrical, moisture, and/or chemical damage.
The package is then mounted, for example on a circuit board or card, for incorporation into any of a wide variety of devices such as computers, cellular telephones, automobiles, appliances, and so forth.
Some leadframe configurations, for example exposed die pad packages, include a separate ground ring structure that is supported around the periphery of the die pad and inside the inner ends of the leads. The ground ring facilitates the many bonding wire electrical connections that typically must be made to connect ground pads on the die to electrical ground connections on the leadframe.
However, leadframes designed with such a ground ring require additional clearance space (i.e., distance) between the die pad and the ground ring and between the ground ring and the inner tips of the peripherally-located leads. This clearance space is necessary for ease of manufacturing and for proper looping of the bonding wires from the die to the ground ring and from the ground ring to the lead tips. Unfortunately, this increases the lengths of the other bonding wires that connect the die to other (e.g., power and signal) leads on the leadframe.
The requirement for ground ring clearance space thus increases the net distance between the die and the lead tips. Typically, there are more wires that connect dies to the power and signal lead tips than to the ground ring and to the ground lead tips. Hence, a ground ring causes the total wire length per die to increase, which correspondingly increases costs. Not only are costs increased, but the additional wire lengths also make the wires prone to sweeping problems during molding. (“Sweeping” of the bonding wires happens during molding of the semiconductor package. Specifically, sweeping happens when the epoxy molding compound pushes the bonding wires out of position as the epoxy molding compound flows past the bonding wires. Sweeping causes bonding wires to short circuit and/or to break.)
Some die pad configurations provide a die pad that is slightly wider than the die and that have continuous grooves in the die pad area just outside the perimeter of the die. The continuous grooves help secure the molding compound to the die pad and thus to the leadframe. However, such continuous grooves contain inadequate space for connecting ground bonds and down bonds to the die pad. The continuous grooves thus effectively prevent ground bonds and down bonds from being attached to the die pad by taking the perimeter die pad area away from such use. In addition, such grooves provide only minor locking of the molding compound to the leadframe, rendering their value and utility only marginal.
As a result, these and other current designs still require a separate ground ring and are therefore subject to the problems of long, looping bonding wires that may lead to wire sweeping, wire shorting, and/or wire breakage during molding.
The separate ground ring also makes wire bonding more difficult because it is not possible to clamp directly onto the ground ring while making the wire bonds. Instead, the ground ring must be held in position indirectly, such as by a device attached to the die pad (e.g., by vacuum suction). The strength of such wire bonds is not as good as the strength of wire bonds made to a surface that is clamped or is held directly by vacuum. These weaker wire bonds increase the rate that the bonding wire connections break during molding, resulting in poor production and manufacturing yields.
Thus, a need still remains for bond separator methods and apparatus for integrated circuit leadframes and packages that will allow space on the die pad that can be used for ground bond and down bond connections, while simultaneously serving, in the same die pad area space, to securely and firmly lock the mold compound to the die pad. Such leadframe bond separator methods and apparatus must provide these advantages and functions without requiring a separate ground ring or increasing manufacturing expenses and costs. In view of the ever increasing complexity and decreasing sizes of integrated circuit dies, it is increasingly critical that answers be found to these problems.
Solutions to these problems have been long sought but prior developments have not taught or suggested any solutions and, thus, solutions to these problems have long eluded those skilled in the art.